The folic acid antimetabolites aminopterin and amethopterin (also known as 10-methylaminopterin or methotrexate) are antineoplastic agents. These compounds inhibit enzymatic conversions involving metabolic derivatives of folic acid. Amethopterin, for example, inhibits dihydrofolate reductase, an enzyme necessary for the regeneration of tetrahydrofolate from dihydrofolate which is formed during the conversion of 2-deoxy-uridylate to thymidylate by the enzyme thymidylate synthetase.
Other derivatives of folic acid and aminopterin have been synthesized and tested as anti-metabolites. Among these are various "deaza" compounds in which a methylene or methylidene group occupies a position in the molecule normally occupied by an imino or nitrilo group, respectively. These derivatives have varying degrees of antimetabolic activity. 10-Deazaaminopterin is highly active (Sirotak et al., Cancer Treat. Rep., 1978, 62, 1047) whereas 10-deazafolic acid shows no significant activity (Struck et al., J. Med. Chem., 1971, 14, 693). 5-Deazafolic acid is only weakly cytotoxic whereas 5-deazaaminopterin has activity similar to that of amethopterin (Taylor et al., J. Org. Chem., 1983, 48, 4852). 5,6,7,8-Tetrahydro-5-deazaaminopterin also is active (U.S. Pat. No. 4,684,653). 8,10-Dideazafolic acid is only marginally effective as a dihydrofolate reductase inhibitor (De Graw et al., "Chemistry and Biology of Pteridines", Elsevier, 1979, 229) while 5,8,10-trideazafolic acid also shows only marginal activity against mouse L1210 leukemia (Oatis et al., J. Med. Chem., 1977, 20, 1393). 8,10-Dideazaaminopterin is reported to be active (U.S. Pat. No. 4,460,591) and 5,8,10-trideazaaminopterin exhibits activity against mouse L1210 leukemia (Yan et al., J. Heterocycl. Chem., 1979, 16, 541).